LOW POWER MEMORY DEVICE
A memory device includes a memory cell unit, a bit line unit and a buffering unit. The memory cell unit includes a plurality of memory cell groups. Each memory cell group includes at least one memory cell for storing data therein. The bit line unit includes a plurality of first bit lines each coupled to the at least one memory cell of a respective memory cell group, and a second bit line for transmitting to-be-read data. The buffering unit includes a plurality of two-state buffers. Each two-state buffer has an input terminal coupled to a respective first bit line, and an output terminal coupled to the second bit line. The memory device does not require a sense amplifier, and thus consumes relatively small power. The memory device can operate at a relatively high frequency when properly configured.
This application claims the priority of Taiwanese Application No. 103111756, filed on 28 Mar. 2014, the disclosure of which is hereby incorporated by reference.
TECHNICAL FIELDThis invention relates to a memory device, and more particularly to a low power memory device.
BACKGROUNDReferring to
The memory cell array 10 includes a plurality of memory cells 13. The word lines 12 intersect the bit lines 11, and are electrically isolated from the bit lines 11. The word lines 12 transmit a control input to the memory cells 13 in order to control the memory cells 13 to output data stored therein to the bit lines 11.
As the demand for storage capacity of memory devices increases, memory cell arrays 10 with many more memory cells 13 would be preferable. However, to accommodate this, each bit line 11 is made longer to be coupled to more memory cells 13, which inevitably increases a capacitance seen thereat.
Because of the relatively large capacitance seen at each bit line 11, voltages outputted by the memory cells 13 may not promptly propagate to the bit lines 11 (i.e., the memory cells 13 may not be able to drive the bit lines 11 efficiently). As a result, a plurality of sense amplifiers 14 are employed to be coupled respectively to the bit lines 11 to assist in amplifying voltages on the bit lines 11 in order to facilitate data transmission and allow the memory device to operate at a higher frequency.
Nonetheless, the sense amplifiers 14 may be undesirable components of the memory device due to their relatively large power consumption. Therefore, it may be beneficial to attempt to address the issue of the capacitance seen at each bit line 11, and to omit the sense amplifiers 14 altogether.
SUMMARYTherefore, an object of this invention is to provide a memory device that does not require a sense amplifier, and that consumes relatively small power.
According to one aspect of this invention, a memory device comprises a memory cell unit, a bit line unit and a buffering unit. The memory cell unit includes a plurality of memory cell groups. Each of the memory cell groups includes at least one memory cell for storing data therein. The bit line unit includes a plurality of first bit lines, each of which is coupled to the at least one memory cell of a respective one of the memory cell groups, and a second bit line for transmitting to-be-read data. The buffering unit includes a plurality of tri-state buffers. Each of the tri-state buffers has an input terminal coupled to a respective one of the first bit lines, and an output terminal coupled to the second bit line.
According to another aspect of this invention, a memory device comprises a memory cell unit, a bit line unit and a buffering unit. The memory cell unit includes a plurality of memory cell groups. Each of the memory cell groups includes at least one memory cell for storing data therein. The bit line unit includes a plurality of first bit lines, each of which is coupled to the at least one memory cell of a respective one of the memory cell groups, and a second bit line for transmitting to-be-read data. The buffering unit includes a plurality of two-state buffers. Each of the two-state buffers has an input terminal coupled to a respective one of the first bit lines, and an output terminal coupled to the second bit line. Each of the two-state buffers is operable between an output enable state and an output disable state based on a voltage at the input terminal, and outputs a predetermined reference voltage at the output terminal when operating in the output enable state.
Other features and advantages of this invention will become apparent in the following detailed description of the preferred embodiments of this invention with reference to the accompanying drawings, of which:
Before this invention is described in greater detail with reference to the accompanying preferred embodiments, it should be noted herein that like elements are denoted by the same reference numerals throughout the disclosure.
Referring to
The memory cell unit 2 includes a plurality of memory cell groups 20. Each memory cell group 20 includes at least one memory cell (MC) 21 for storing data therein. In this embodiment, the memory cell unit 2 is in the form of a memory cell line and includes, for example, thirty-two (32) memory cell groups 20, and each memory cell group 20 includes, for example, eight (8) memory cells 21. That is, the total number of the memory cells is, for example, two-hundred-and-fifty-six (256). However, it should be noted that the memory cell groups 20 do not necessarily have to have equal numbers of memory cells 21 in other embodiments of this invention.
The bit line unit 3 includes a plurality of first bit lines 31 each coupled to the memory cells 21 of a respective memory cell group 20, a second bit line 32 for transmitting to-be-read data, a third bit line 41 for transmitting to-be-written data, and a plurality of fourth bit lines 42 each coupled to the memory cells 21 of a respective memory cell group 20.
The buffering unit 5 includes a plurality of tri-state buffers 51. Each tri-state buffer 51 has an input terminal coupled to a respective first bit line 31, and an output terminal coupled to the second bit line 32. Each tri-state buffer 51 is operable between an output enable state and an output disable state, outputs one of two predetermined reference voltages (e.g., a logic high voltage and a logic low voltage) at the output terminal based on a voltage at the input terminal when operating in the output enable state, and does not output any voltage at the output terminal (i.e., exhibiting high impedance at the output terminal) when operating in the output disable state.
In this embodiment, each tri-state buffer 51 is a buffer that is activated and deactivated in the output enable state and the output disable state, respectively. However, as shown in
Referring back to
Each first switch 52 is coupled between the third bit line 41 and a respective fourth bit line 42. In this embodiment, each first switch 52 is an N-channel metal oxide semiconductor field effect transistor (MOSFET) (see
It is noted that the first switches 52 and the fourth bit lines 42 may be omitted in other embodiments. In this case, as shown in
Referring back to
It is noted that each of the first and second predetermined bias voltages may be the logic high voltage or the logic low voltage, depending on the configuration of the memory cells 21. Moreover, the second biasing circuit 62 may be omitted in other embodiments, in which case the second bit line 32 is adapted to be coupled to an external circuit that can supply the second predetermined bias voltage thereto.
In operation, when one of the memory cells 21 is selected to have data written thereinto, the corresponding first switch 52 is turned on while the other first switches 52 remain turned off, such that the data is written into the selected memory cell 21 through the third bit line 41, the corresponding first switch 52 and the corresponding fourth bit line 42. When one of the memory cells 21 is selected to have data stored therein be read, the corresponding tri-state buffer 51 switches to the output enable state while the other tri-state buffers 51 remain in the output disable state, such that the data stored in the selected memory cell 21 is read through the corresponding first bit line 31, the corresponding tri-state buffer 51 and the second bit line 32.
It is noted that, in this embodiment, each memory cell 21 is read and written at different terminals. However, in other embodiments, each memory cell 21 may be read and written at the same terminal, in which case the fourth bit lines 42 are omitted, and each first switch 52 is coupled to a respective first bit line 31 instead.
In view of the above, the memory device of this embodiment shown in
1. Since each first bit line 31 is relatively short and is coupled to a relatively small number (i.e., 8 instead of 256) of memory cells 21, a capacitance seen thereat can be reduced to 1/32 that of the conventional memory device (see
2. Since each tri-state buffer 51 assists in driving the second data line 32, a sense amplifier is not required, thereby reducing overall power consumption of the memory device of this embodiment.
3. By using a driving circuit (not shown) with a large driving capability to drive the third bit line 41, a time constant of the third bit line 41 can approximate that of each first bit line 31. Therefore, the memory device of this embodiment can be read and written at the same order of frequency.
4. Since each first biasing circuit 61 supplies the first predetermined bias voltage to the input terminal of the respective tri-state buffer 51 when none of the memory cells 21 of the respective memory cell group 20 is read, the input terminal of each tri-state buffer 51 will not be floating, thereby preventing unnecessary power consumption by the memory device of this embodiment.
Moreover, for each of the memory devices shown respectively in
Referring to
Each two-state buffer 53 is operable between an output enable state and an output disable state based on a voltage at the input terminal, outputs a predetermined reference voltage at the output terminal when operating in the output enable state, and does not output any voltage at the output terminal (i.e., exhibiting high impedance at the output terminal) when operating in the output disable state.
The predetermined reference voltage may be the logic high voltage or the logic low voltage depending on design choice. Each two-state buffer 53 may be a transistor (e.g., a FET such as a MOSFET or a FinFET) that has a first terminal (e.g., one of a source terminal and a drain terminal) for receiving the predetermined reference voltage, a second terminal (e.g., the other of the source terminal and the drain terminal) serving as the output terminal, and a control terminal (e.g., a gate terminal) serving as the input terminal, and that is turned on and off to bring the two-state buffer 53 in the output enable state and the output disable state, respectively.
In a first example, as shown in
In a second example, as shown in
In a third example, as shown in
In a fourth example, as shown in
Referring back to
Each of the first and second predetermined bias voltages may be the logic high voltage or the logic low voltage. When each two-state buffer 53 has the configuration shown in
Similarly, when each two-state buffer 53 has the configuration shown in
Referring back to
It is noted that in other embodiments, the following modifications may be made to the second preferred embodiment:
1. The second switches 7 may be omitted. In this case, the input terminal of each two-state buffer 53 is coupled to the respective first bit line 31.
2. The first switches 52 and the fourth bit lines 42 may be omitted. In this case, as shown in
In view of the above, the memory device of this embodiment further has the following advantages:
1. Since the configuration of the two-state buffer 53 is simpler than that of the tri-state buffer 51 (see
2. Since all of the second switches 7 are turned off and thus the voltage at the input terminal of each two-state buffer 53 remains unchanged when none of the memory cells 21 is read, unnecessary power consumption by the memory device can be prevented even if any of the memory cells 21 outputs the data stored therein at this time.
While this invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
Claims
1. A memory device comprising:
- a memory cell unit including a plurality of memory cell groups, each of said memory cell groups including at least one memory cell for storing data therein;
- a bit line unit including a plurality of first bit lines, each of which is coupled to said at least one memory cell of a respective one of said memory cell groups, and a second bit line for transmitting to-be-read data; and
- a buffering unit including a plurality of two-state buffers, each of said two-state buffers having an input terminal coupled to a respective one of said first bit lines, and an output terminal coupled to said second bit line, each of said two-state buffers being operable between an output enable state and an output disable state based on a voltage at said input terminal, and outputting a predetermined reference voltage at said output terminal when operating in the output enable state.
2. The memory device of claim 1, wherein each of said two-state buffers is a transistor that has a first terminal for receiving the predetermined reference voltage, a second terminal serving as said output terminal, and a control terminal serving as said input terminal.
3. The memory device of claim 1, wherein each of said two-state buffers is a field effect transistor that has a source terminal, a drain terminal and a gate terminal, one of said source and drain terminals receiving the predetermined reference voltage, the other of said source and drain terminals serving as said output terminal, said gate terminal serving as said input terminal.
4. The memory device of claim 1, further comprising a biasing unit that is coupled to said input terminal of each of said two-state buffers for supplying a predetermined bias voltage thereto.
5. The memory device of claim 1, further comprising a biasing unit that is coupled to said second bit line for supplying a predetermined bias voltage thereto.
6. The memory device of claim 1, wherein each of said memory cell groups further includes a dummy cell that is coupled to a respective one of said first bit lines for supplying a predetermined bias voltage thereto.
7. The memory device of claim 1, wherein one of said at least one memory cell of each of said memory cell groups outputs the data stored therein to bias a corresponding one of said first bit lines.
8. The memory device of claim 1, further comprising a plurality of switches, each of said switches being coupled between said input terminal of a respective one of said two-state buffers and a respective one of said first bit lines.
9. The memory device of claim 1, further comprising a plurality of switches, each of said switches being coupled between said output terminal of a respective one of said two-state buffers and said second bit line.
10. The memory device of claim 1, wherein said bit line unit further includes a third bit line that is coupled to said at least one memory cell of each of said memory cell groups and that transmits to-be-written data.
11. The memory device of claim 1, further comprising a plurality of switches;
- wherein said bit line unit further includes a third bit line for transmitting to-be-written data, and a plurality of fourth bit lines, each of which is coupled to said at least one memory cell of a respective one of said memory cell groups; and
- wherein each of said switches is coupled between said third bit line and a respective one of said fourth bit lines.
12. The memory device of claim 1, further comprising a plurality of switches;
- wherein each of said switches is coupled between a respective one of said first bit lines and said second bit line; and
- wherein said second bit line further transmits to-be-written data.
13. A memory device comprising:
- a memory cell unit including a plurality of memory cell groups, each of said memory cell groups including at least one memory cell for storing data therein;
- a bit line unit including a plurality of first bit lines, each of which is coupled to said at least one memory cell of a respective one of said memory cell groups, and a second bit line for transmitting to-be-read data; and
- a buffering unit including a plurality of tri-state buffers, each of said tri-state buffers having an input terminal coupled to a respective one of said first bit lines, and an output terminal coupled to said second bit line.
14. The memory device of claim 13, further comprising a biasing unit that is coupled to said input terminal of each of said tri-state buffers for supplying a predetermined bias voltage thereto.
15. The memory device of claim 13, further comprising a biasing unit that is coupled to said second bit line for supplying a predetermined bias voltage thereto.
16. The memory device of claim 13, wherein each of said memory cell groups further includes a dummy cell that is coupled to the respective one of said first bit lines for supplying a predetermined bias voltage thereto.
17. The memory device of claim 13, wherein one of said at least one memory cell of each of said memory cell groups outputs the data stored therein to bias a corresponding one of said first bit lines.
18. The memory device of claim 13, wherein said bit line unit further includes a third bit line that is coupled to said at least one memory cell of each of said memory cell groups, and that transmits to-be-written data.
19. The memory device of claim 13, further comprising a plurality of switches;
- wherein said bit line unit further includes a third bit line for transmitting to-be-written data, and a plurality of fourth bit lines, each of which is coupled to said at least one memory cell of a respective one of said memory cell groups; and
- wherein each of said switches is coupled between said third bit line and a respective one of said fourth bit lines.
20. The memory device of claim 13, further comprising a plurality of switches;
- wherein each of said switches is coupled between a respective one of said first bit lines and said second bit line; and
- wherein said second bit line further transmits to-be-written data.
21. The memory device of claim 13, wherein for each of said tri-state buffers, a voltage at said output terminal is anti-phase with a voltage at said input terminal.
Type: Application
Filed: Jun 27, 2014
Publication Date: Oct 1, 2015
Patent Grant number: 9431073
Inventor: Chih-Cheng HSIAO (Taichung City)
Application Number: 14/318,506